The present invention relates to fluid pressure actuated grippers of the type employed in automated workpiece handling devices which clampingly grip and transfer workpieces from one station to another. More particularly, the present invention relates to a continuity switch assembly for fluid pressure actuated grippers.
Fluid pressure actuated grippers are widely employed and typically take the form of a pneumatic or hydraulic differential motor whose cylinder is fixedly mounted to a transfer device. At the forward or rod end of the cylinder housing, a gripper jaw mounting structure is fixedly mounted on the cylinder to pivotally support a pair of opposed gripper jaws which are coupled to the piston rod of the motor by a linkage so arranged that, upon movement of the piston in one direction, the jaws are pivoted to an open position, and upon movement of the piston in the opposite direction, the jaws are driven to a closed workpiece gripping position.
In typical operation, the gripper jaws will be closed upon a workpiece near the edge of the workpiece, and the gripper will be advanced to position the gripped workpiece in operative relationship with a work station. The gripper will then be opened to release the workpiece, and the transfer device will retract the gripper from the work station while the work operation is performed. At the conclusion of the work operation, the gripper will then advance back into the work station, and the jaws will again close upon the workpiece and carry it away from the work station. Opening and closing the gripper jaws thus takes place when the gripper is in its closest proximity to tooling at the work station.
There are basically two types of linkage arrangements used in fluid pressure actuated grippers to connect the gripper jaws to the piston rods and effect movement of the gripper jaws. These are pivotable link arrangements and pivotal cam arrangements. An example of a pivotal link arrangement can be found in U.S. Pat. No. 5,152,568 to Blatt, which discloses pivotal links 36 and 40 that cooperate with gripper jaws 12A and 12B, as shown in FIG. 3.
U.S. Pat. No. 4,518,187 to Blatt, et al. discloses a pivotal cam arrangement in which jaw plates 45 and 47 are pivoted by the cooperation of cam slots 61 provided in the jaw plates and a pivot pin 37 (and rollers 39) attached to the piston rod.
In a typical production line, there are numerous work stations with one or more fluid pressure actuated gripper devices positioned between adjacent work stations. During operation, all of the gripper devices are synchronized so that they simultaneously remove a workpiece from one work station and transfer the workpiece to the next work station. In such an operation, a problem can occur if any one of the gripper devices fails to properly grip a workpiece. For example, if a workpiece slips from its initial gripped position, it can become sufficiently out of alignment to prevent its transfer to a succeeding gripper device. A more serious problem can occur if a workpiece is transferred in a misaligned manner and, subsequently, positioned at a work station in a misaligned fashion. Such an incident can damage the work station. Another problem which can occur is completely losing grip of a workpiece and dropping the workpiece. Losing grip of a workpiece can occur when there is a leak or failure of fluid pressure supplied to the piston rod actuator.
The present invention provides a continuity switch for parts grippers that can be used to determine the presence of a part or workpiece held between the jaws of a parts gripper.
One embodiment of the present invention provides a parts gripper comprising a gripper body having a yoke, a pair of jaw members, a pivot pin, and an electrical lead conductively connected to the pivot pin. The pivot pin has a shaft conductively connected to the jaw members and connects the jaw members to the yoke of the gripper body.
In one embodiment of the parts gripper, the pivot pin includes a neck portion having a radius smaller than the radius of the shaft.
In another embodiment of the parts gripper, the parts gripper further includes a cover plate. The cover plate has a keyed through-hole for mating with the neck of the pivot pin.
In yet another embodiment of the parts gripper, the keyed through-hole includes a first portion with a first radius and a second portion with a second radius. The first radius is greater than the radius of the shaft, and the second radius is greater than the radius of the neck portion and less than the radius of the shaft portion.
In still another embodiment of the parts gripper, the pivot pin includes a stepped portion with a width greater than the width of the shaft.
In another embodiment of the parts gripper, the gripper further comprises a side impact plate having a slot for mating with the stepped portion of the pivot pin to prevent the pivot pin from rotating.
In yet another embodiment of the parts gripper, the width of the stepped portion of the pivot pin is approximately equal to the width of the slot of the side impact plate.
In still another embodiment of the parts gripper, the pivot pin includes an attachment portion for connecting the electronic lead.
In yet another embodiment of the parts gripper, the attachment portion of the pivot pin is threaded and includes a threaded nut to connect the electrical lead thereon.
A second embodiment of the present invention provides a parts gripper comprising a parts gripper body having a yoke, a pair of jaw members, a pivot pin, a cover plate, a side impact plate, and an electrical lead conductively connected to the first attachment portion of the pivot pin. The pivot pin is conductively connected to the jaw members and connects the jaw members to the yoke of the gripper body. The pivot pin includes a shaft, a neck portion, a stepped portion, and a first attachment portion. The shaft connects the jaw members to the yoke. The cover plate has a keyed through-hole for mating with the neck portion of the pivot pin. The side impact plate has a slot for mating with the stepped portion of the pivot pin to prevent the pivot pin from rotating.
In one embodiment of the parts gripper, the keyed through-hole includes a first portion with a first radius and a second portion with a second radius, the first radius being greater than the second radius.
In another embodiment of the parts gripper, the neck portion of the pivot pin has a radius smaller than the radius of the shaft of the pivot pin.
In yet another embodiment of the parts gripper, the width of the stepped portion of the pivot pin is approximately equal to the width of the slot of the side impact plate.
In still another embodiment of the parts gripper, the stepped portion of the pivot pin includes at least one flat side.
In yet another embodiment of the parts gripper, the side impact plate includes at least one leg.
In another embodiment of the parts gripper, the pivot pin includes a second attachment portion disposed opposite the first attachment portion.
In yet another embodiment of the parts gripper, the first attachment point is threaded and includes a threaded nut to connect the electrical lead thereon.
A third embodiment of the present invention provides a work station for positioning a workpiece. The work station comprises a pair of parts grippers, a continuity detector, a first electrical lead, and a second electrical lead. Each of the parts grippers has a pair of jaw members for grabbing the workpiece and a pivot pin having a shaft conductively connected to the jaw members. The continuity detector has a pair of inputs for determining the presence of the workpiece between the jaw members of the parts grippers. The first electrical lead connects the pivot pin of one of the parts grippers to one of the inputs of the continuity detector. The second electrical lead connects the pivot pin of the other parts gripper to the other input of the continuity detector.
In another embodiment of the work station, each pivot pin includes a neck portion, a stepped portion, and an attachment portion. The radius of the neck portion is less than the radius of the neck portion, and the width of the stepped portion is greater than the width of the shaft.
In yet another embodiment of the work station, each parts gripper includes a cover plate and a side impact plate. The cover plate includes a keyed through-hole that mates with the neck portion of the pivot pin. The side impact plate includes a slot that mates with the stepped portion of the pivot pin.